The present invention relates generally to apparatus for magnifying the image from a cathode ray tube and, more particularly, is directed to a television magnification apparatus providing improved resolution.
Television projection systems in which the image from the screen of a conventional television receiver is magnified and then projected on a flat surface are well known in the art. One such system uses a single Fresnel lens to magnify and project the image.
For example, such a system is shown and described in U.S. Pat. No. 4,074,322. As shown and described therein, a fixed housing is removably mounted to the front of a television receiver. A movable housing is slidably mounted within the fixed housing and contains a single Fresnel lens and at least one reflecting mirror. See also U.S. Pat. Nos. 2,260,228; 3,525,807 and 4,439,027 and British Patent No. 680,916 for other single Fresnel lens systems.
With single Fresnel lens systems, however, it becomes difficult to obtain clear and sharp projected images, regardless of focusing adjustments that are provided by permitting sliding movement of the single Fresnel lens, for example, by the movable housing of U.S. Pat. No. 4,074,322. See also U.S. Design Pat. No. 257,039 with respect to a movable housing.
Other systems have been provided which use three or more Fresnel lenses. For example, U.S. Pat. No. 4,457,594 requires the use of three Fresnel lenses, while U.S. Pat. No. 4,391,495 requires the use of five Fresnel lenses in a complicated arrangement. See also U.S. Pat. No. 3,800,085 which uses five irregularly configured lenses. Although it is possible that these systems may provide a clearer and sharper image than that provided by a single Fresnel lens system, the time required to manufacture and the cost of the assembly is greatly increased.
It will be noted that U.S. Pat. No. 4,309,074, which discloses a viewing screen designed to produce a three dimensional effect, uses two Fresnel lenses in back to back relation to form a conventional biconvex lens. Basically, the Fresnel lenses are thin and flexible, and are vibrated by acoustic waves to produce the three dimensional effect. However, there is no projection and magnification of an image, and the system is not used as a projection television.